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MT1000:O/P xtrs substitution


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#1 mystuffisold

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Posted 03 July 2006 - 09:23 PM

I've repaired one of my own MT1000s. 6492-#3 PNP O/Ps are no longer available, so I had to use #2 grade. I replaced all 6 devices (ch2) and made all bias and ODEP adjustments as per the service manual. Everything falls within spec. ( original NPN devices are #2s) My concern is the whether the ODEP sensor S200 should have have been changed to a different grade because of the O/P transistor substitution? I've performed all the QC tests and have been bench testing the amp. All seems to be well. Am I OK with with the change to 6492-#2 in place of the original #3s without replacing any other components?
Please advise.

Thanks
JC

#2 joust

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Posted 08 July 2006 - 01:17 PM

I have never found that it was necessary to replace the S200 sensor when replacing output devices. Though, if the amp is older than 7 years old, I highly recommend a full output maintenance: cleaning and reapplication of thermal compound to all output devices making contact with the heatsink (output devices, drivers, thermal sensors and bias transistor). This will definitively improve thermal dissipation and ODEP monitoring. smile.gif Also, replace the bias trims: it should improve bias calibration and efficiency.